A mesa is an isolated, flat-topped elevation, ridge or hill, which is bounded from all sides by steep escarpments and stands distinctly above a surrounding plain. Mesas characteristically consist of flat-lying soft sedimentary rocks capped by a more resistant layer or layers of harder rock, e.g. shales overlain by sandstones. The resistant layer acts as a caprock that forms the flat summit of a mesa. The caprock can consist of either sedimentary rocks such as sandstone and limestone; dissected lava flows; or a deeply eroded duricrust. Unlike plateau, whose usage does not imply horizontal layers of bedrock, e.g. Tibetan Plateau, the term mesa applies exclusively to the landforms built of flat-lying strata. Instead, flat-topped plateaus are specifically known as tablelands.
Yuanzhou District, which belongs to Guyuan City, Ningxia Hui Autonomous region, is located in the south of Ningxia, the northeast foot of Liupan Mountain and the central and western part of the Loess Plateau. It lies between 105 °28 degrees east longitude and 106 °30 'east longitude and 36 °38 degrees north latitude. It is bordered by Pengyang County in the east, Jingyuan County in the south, Xiji County in the west, Haiyuan County and Tongxin County in the north, and Huanxian County and Longde County in Gansu Province in the northeast and southwest, respectively. With a total area of 2739.01 square kilometers, it has jurisdiction over 3 streets, 7 towns and 4 townships. As of 2017, the total number of registered households in Yuanzhou District is 156100, and the total registered population is 464800. In 2017, Yuanzhou District achieved a GDP of 11.766 billion yuan, exceeding 11 billion yuan for the first time. September 2017